U.S. patent application number 13/645643 was filed with the patent office on 2014-04-10 for mitigation of interfence from a mobile relay node to heterogeneous networks.
This patent application is currently assigned to TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Gary David BOUDREAU, Konstantinos DIMOU.
Application Number | 20140099881 13/645643 |
Document ID | / |
Family ID | 49886984 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140099881 |
Kind Code |
A1 |
BOUDREAU; Gary David ; et
al. |
April 10, 2014 |
MITIGATION OF INTERFENCE FROM A MOBILE RELAY NODE TO HETEROGENEOUS
NETWORKS
Abstract
Devices, systems and methods for mitigating the interference
introduced by mobile relay nodes in a heterogeneous network are
described. The techniques described apply fractional frequency
reuse and power controlled beamforming to mitigate such
interference.
Inventors: |
BOUDREAU; Gary David;
(Kanata, CA) ; DIMOU; Konstantinos; (Stockholm,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Assignee: |
TELEFONAKTIEBOLAGET L M ERICSSON
(PUBL)
Stockholm
SE
|
Family ID: |
49886984 |
Appl. No.: |
13/645643 |
Filed: |
October 5, 2012 |
Current U.S.
Class: |
455/7 |
Current CPC
Class: |
H04W 16/32 20130101;
H04W 16/10 20130101; H04B 7/0617 20130101; H04B 7/14 20130101; H04W
72/0453 20130101; H04W 52/46 20130101; H04W 16/28 20130101 |
Class at
Publication: |
455/7 |
International
Class: |
H04B 7/14 20060101
H04B007/14 |
Claims
1. A method, stored in a memory and executing on a processor, for
mitigating interference associated with transmissions on radio
access links and wireless backhaul links of mobile relay nodes,
said method comprising: applying fractional frequency reuse between
the radio access links and the wireless backhaul links associated
with said mobile relay nodes; and applying power controlled
targeted beamforming to the wireless backhaul links associated with
the mobile relay nodes.
2. The method of claim 1, wherein said fractional frequency reuse
is applied within a donor macro cell having an associated,
stationary base station.
3. The method of claim 2, wherein said power controlled targeted
beamforming is applied on said wireless backhaul links between said
mobile relay nodes and the associated, stationary base station.
4. The method of claim 3, wherein the step of applying fractional
frequency reuse further comprises: assigning a first group of
dedicated frequency resource blocks to said wireless backhaul links
between said mobile relay nodes and said base station; and
assigning a second group of dedicated frequency resource blocks to
said radio access links of said mobile relay nodes.
5. The method of claim 4, wherein said first group of dedicated
frequency resource blocks and said second group of dedicated
resource blocks can be assigned across the entire available
frequency band.
6. The method of claim 1, wherein said wireless backhaul links and
said radio access links comprise both an uplink and a downlink.
7. The method of claim 3, further comprising: adjusting power
associated with a wireless backhaul link as a mobile relay node
changes geographical position with respect to the associated,
stationary base station.
8. The method of claim 7, wherein said adjusting is performed based
on at least one of: (a) a Reference Signal Received Power (RSRP)
metric of a Channel State Information (CSI) Reference Signal (RS)
at said mobile relay node; (b) a Reference Signal Received Quality
(RSRQ) metric of a Channel State Information (CSI) Reference Signal
(RS) at said mobile relay node; (c) maximizing a Signal-to-Noise
Leakage Ratio (SLNR) metric; (d) data associated with a Physical
Uplink Shared Channel (PUSCH) at said associated, stationary base
station while said mobile relay node is transmitting; (e) data
associated with a Physical Uplink Control Channel (PUCCH) at said
associated, stationary base station while said mobile relay node is
transmitting; (f) data associated with a Sounding Reference Signal
(SRS) at said associated, stationary base station while said mobile
relay node is transmitting;
9. The method of claim 3, further comprising: assigning a unique
Channel State Information (CSI) Reference Signal (RS) to each
mobile relay node to allow said associated, stationary base station
to differentiate between each of a plurality of mobile relay nodes
associated with the donor macro cell.
10. The method of claim 9, wherein said step of applying power
controlled targeted beamforming further comprises: allocating a
different frequency partition for each of the wireless backhaul
links between said mobile relay nodes and an associated, stationary
base station.
11. The method of claim 1, wherein said fractional frequency reuse
is implemented between donor macro cells each of which have an
associated, stationary base station.
12. The method of claim 11, wherein first wireless backhaul links
associated with mobile relay nodes connected to a first one of the
associated, stationary base stations and second wireless backhaul
links associated with mobile relay nodes connected to a second one
of the associated, stationary base stations are isolated from each
other by assigning separate frequency partitions to first wireless
backhaul links and the second wireless backhaul links.
13. The method of claim 12, further comprising the step of:
assigning a unique Channel State Information (CSI) Reference Signal
(RS) to each mobile relay node within a donor macro cell to allow
said associated, stationary base station to differentiate between
each of a plurality of mobile relay nodes located within the donor
macro cell.
14. The method of claim 13, wherein said assigning is coordinated
between said associated, stationary base stations.
15. The method of claim 11, further comprising: assigning temporary
guard bands to separate transmissions on the wireless backhaul
links from transmissions on the radio access links.
16. The method of claim 11, wherein a number of resource blocks
assigned for wireless backhaul links and radio access links are not
equal.
17. The method of claim 11, wherein frequency partition boundaries
are dynamically assigned based on predicted relative proportional
traffic for a partition.
18. The method of claim 17, wherein the predicted relative
proportional traffic is an offered traffic load within a frequency
partition divided by available capacity of an associated link.
19. The method of claim 1, wherein either or both of the steps of
applying fractional frequency reuse and applying power controlled
targeted beamforming are triggered in response to the occurrence of
one or more predetermined criteria.
20. The method of claim 1, wherein said mobile relay node
establishes a wireless backhaul link to the geographically closest
stationary node of a heterogeneous network.
21. A node usable in a radio communication system which mitigates
interference associated with transmissions on radio access links
and wireless backhaul links, said node comprising: a processor and
transceiver which are configured to apply fractional frequency
reuse between the radio access links and the wireless backhaul
links associated with mobile relay nodes, and wherein said
processor and transceiver are further configured to apply power
controlled targeted beamforming to the wireless backhaul links
associated with the mobile relay nodes.
22. The node of claim 21, wherein said fractional frequency reuse
is applied within a donor macro cell having an associated,
stationary base station which is said node.
23. The node of claim 22, wherein said power controlled targeted
beamforming is applied on said wireless backhaul links between said
mobile relay nodes and the associated, stationary base station.
24. The node of claim 23, wherein the processor and transceiver are
further configured to apply fractional frequency reuse by:
assigning a first group of dedicated frequency resource blocks to
said wireless backhaul links between said mobile relay nodes and
said base station; and assigning a second group of dedicated
frequency resource blocks to said radio access links of said mobile
relay nodes.
25. The node of claim 24, wherein said first group of dedicated
frequency resource blocks and said second group of dedicated
resource blocks can be assigned across the entire available
frequency band.
26. The node of claim 24, wherein the processor is further
configured to adjust power associated with a wireless backhaul link
as a mobile relay node changes geographical position with respect
to the associated, stationary base station.
27. The node of claim 26, wherein said adjusting is performed based
on at least one of: (a) a Reference Signal Received Power (RSRP)
metric of a Channel State Information (CSI) Reference Signal (RS)
at said mobile relay node; (b) a Reference Signal Received Quality
(RSRQ) metric of a Channel State Information (CSI) Reference Signal
(RS) at said mobile relay node; (c) maximizing a Signal-to-Noise
Leakage Ratio (SLNR) metric; (d) data associated with a Physical
Uplink Shared Channel (PUSCH) at said associated, stationary base
station while said mobile relay node is transmitting; (e) data
associated with a Physical Uplink Control Channel (PUCCH) at said
associated, stationary base station while said mobile relay node is
transmitting; (f) data associated with a Sounding Reference Signal
(SRS) at said associated, stationary base station while said mobile
relay node is transmitting;
28. A mobile wireless relay node comprising: a housing configured
to be mounted on a movable platform; at least one transceiver
configured to transmit and receive radio signals (a) to and from a
donor macro base station over a wireless backhaul link and (b) to
and from at least one user equipment over a radio access link; and
wherein the at least one transceiver is further configured to apply
fractional frequency reuse to the transmission and reception of
radio signals associated with the wireless backhaul link.
29. The mobile wireless relay node of claim 28, wherein the at
least one transceiver is further configured to apply power
controlled targeted beamforming in an uplink of the wireless
backhaul link.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to reducing
interference in wireless communications systems and more
specifically to reducing interference from a mobile relay node in
heterogeneous wireless networks.
BACKGROUND
[0002] The constantly increasing demand for higher data rates in
cellular networks requires new approaches to meet the demand.
Different mechanisms have evolved for increasing the data rates of
cellular networks such as increasing the density of the macro base
stations (BS), increasing the cooperation between the macro base
stations and deploying smaller base stations or relay nodes (RN) in
areas where high data rates are required within the macro base
station grid. The option of deploying smaller base stations or
relay nodes in the macro base station grid is generally referred to
as a heterogeneous deployment (creating a heterogeneous network)
and the layer of smaller base stations is known as a micro-layer or
pico-layer depending on the characteristics of the smaller base
stations.
[0003] Although each of the above-described choices would result in
increasing the data rates of a cellular network, economics
associated with those choices typically dictate that creating a
heterogeneous network would be the most cost-effective
implementation. Further, the implementation time frames requested
by operators also seems to favor heterogeneous network solutions.
As an example of heterogeneous deployment, and looking to FIGS. 1a
and 1b, a homogeneous cellular network 100 can be illustrated as a
collection of cells 102, 104, 106, 108, 110, each of which
represent the radio communication coverage area of a macro base
station. FIG. 1b illustrates an exemplary heterogeneous network
where cells 102, 104, 106, 108, 110 still provide radio
communication coverage via their respective macro base stations,
but where that coverage is augmented by the provision of micro/pico
base stations 112, 114, 116 within the cell areas of macro base
stations 102, 104, 110, respectively, by way of a heterogeneous
deployment.
[0004] One of the objectives of creating heterogeneous networks is
to allow the micro/pico base stations to offload as many users as
possible from the macro layer, allowing higher data rates in both
the macro layer and the micro/pico layer. To this end, different
techniques have been proposed for increasing the capacity of the
micro/pico base stations. First, capacity can be increased by
extending the range of the micro/pico base stations using cell
specific cell selection offsets. Cell selection offsets are one
factor used to determine whether a user equipment should connect to
the heterogeneous network via a micro/pico base station or a macro
base station. Second, capacity can be increased by simultaneously
increasing the transmission power of the micro/pico base stations
and appropriately setting the uplink (UL) power control target
(P.sub.0) for the users connected to the micro/pico base
stations.
[0005] Under certain circumstances, e.g., prohibitive backhaul
costs associated with adding a micro/pico base station, a relay
node (RN) can provide a viable solution to provide increased range
and/or capacity based its usage of an in-band (wireless) backhaul.
The relay node can provide pico base station type coverage either
indoors or outdoors and mitigate the cost and effort of deploying
land-line backhaul to all of the pico base stations. In a further
scenario, there are users on mobile platforms, i.e.,
commuter/passenger trains that would benefit from a mobile relay
node. The implementation of a mobile relay node involves local
access from the mobile relay node to the users on the mobile
platform and in-band backhaul bandwidth from the mobile relay node
to a stationary serving macro base station or an eNB.
[0006] A problem identified with heterogeneous networks employing
relay nodes is that the backhaul link (Un) between the serving or
donor base station and the relay node can generate additional
interference, above normally expected levels, in the macro network.
The increased interference can reduce the capacity of the macro
network, therefore undermining the intent of creating the
heterogeneous network. For example, as depicted in FIG. 2a, Un
uplink transmissions 208 to a given macro base station 204 from a
relay node 210 can cause interference 212 in the backhaul Un uplink
transmissions 214 of relay nodes 216 in adjacent macro base
stations 202. Furthermore, the Un uplink transmissions 208 from
relay nodes 210 within one macro base station cell 218 can
interfere 220 with uplink transmissions between the terminals or
user equipment (UE) 222 to their serving relay nodes 224 in
neighboring macro base station cells 226.
[0007] A reciprocal problem can occur wherein the downlink (DL)
transmission on the Uu link can cause interference in the downlink
Un link of neighboring cell relay nodes. It should be noted that
these scenarios are likely to occur because typical deployments for
relay nodes are those in which the relay nodes are placed at cell
edges of neighboring donor macro base stations, thus resulting in
the placement of relay nodes supporting adjacent macro base
stations in close proximity to each other. Considering mobile relay
nodes, the potential interference scenarios are further exacerbated
when the mobile relay node moves closer to the serving eNB of the
donor macro cell. In this mobile relay node scenario, the user
equipment associated with the donor macro cell that are near the
edge of the donor macro cell can be severely interfered with by the
backhaul Un link of the mobile relay node to the donor eNB.
Furthermore, if the mobile relay node gets too close to the donor
eNB it could completely desensitize the front end of the donor eNB
and cause an outage to all of the users served by the donor
eNB.
[0008] Considering LTE networks, the existing approach to
mitigating this type of interference involves time multiplexing of
the Un and Uu transmissions within a donor macro cell to reduce the
potential Un to Uu interference. The two main issues with this type
of interference mitigation approach are first, the time
multiplexing reduces the interference within a given donor macro
cell but it does not guarantee reduction of interference between
relay nodes of adjacent macro donor cells, with the problem being
aggravated by the mobility of the relay node and second, even
though the relay node can use directive antennas for the Un link,
the side lobes and/or back lobe of the relay node antenna for the
Un link can still cause significant interference to a relay node's
Uu link in neighboring macro donor cells. This latter issue is most
apparent when a mobile relay node is in close proximity to the
donor eNB or a remote radio head (RRH) of the serving macro donor
cell.
[0009] It should be noted that the above described situation in an
LTE network can occur when mobile relay nodes are deployed near the
edge of neighboring macro donor cells, which, as described above,
is the most like position for deployment of mobile relay nodes.
Although in theory, restrictions in the time domain regarding when
neighboring macro donor cell's relay nodes can transmit on their Un
and Uu links might be sufficient to mitigate interference, this
would require strict time synchronization between neighboring macro
donor cells and the mobile relay nodes within the neighboring donor
macro cells and in general, cellular networks may not be time
synchronized.
[0010] Accordingly, efforts for a method of reducing interference
in unsynchronized cellular networks deploying mobile relay nodes
are of importance to service providers and indirectly to the
customers accessing the cellular network.
SUMMARY
[0011] Embodiments described herein provide for mitigation of
interference between wireless backhaul links and radio access links
(as well as among wireless backhaul links themselves) in
heterogeneous radio communication networks employing mobile relay
nodes. Embodiments mitigate interference both within donor cells,
as well as between donor cells in a heterogeneous network, and do
not require explicit synchronization between neighboring cells.
[0012] According to an exemplary embodiment, a method, stored in a
memory and executing on a processor, for mitigating interference
associated with transmissions on radio access links and wireless
backhaul links of mobile relay nodes is described. Fractional
frequency reuse is applied between the radio access links and the
wireless backhaul links associated with said mobile relay nodes.
Power controlled targeted beamforming is applied to the wireless
backhaul links associated with the mobile relay nodes.
[0013] According to another embodiment, a node usable in a radio
communication system which mitigates interference associated with
transmissions on radio access links and wireless backhaul links
includes a processor and transceiver which are configured to apply
fractional frequency reuse between the radio access links and the
wireless backhaul links associated with mobile relay nodes, and
wherein the processor and transceiver are further configured to
apply power controlled targeted beamforming to the wireless
backhaul links associated with the mobile relay nodes.
[0014] According to another embodiment, a mobile wireless relay
node includes a housing configured to be mounted on a movable
platform, at least one transceiver configured to transmit and
receive radio signals (a) to and from a donor macro base station
over a wireless backhaul link and (b) to and from at least one user
equipment over a radio access link; and wherein the at least one
transceiver is further configured to apply fractional frequency
reuse to the transmission and reception of radio signals associated
with the wireless backhaul link.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings illustrate exemplary embodiments,
wherein:
[0016] FIG. 1a depicts a homogeneous network and FIG. 1b depicts a
heterogeneous network;
[0017] FIG. 2a depicts a heterogeneous network with typical
interference associated with mobile relay nodes;
[0018] FIG. 2b illustrates various aspects associated with relay
nodes;
[0019] FIG. 3a depicts a mapping of frequency partition to mobile
relay node spatial deployment for intra-cell Un to Uu Fractional
Frequency Reuse (FFR) according to an exemplary embodiment;
[0020] FIG. 3b depicts a frequency domain FFR partitioning
according to an exemplary embodiment;
[0021] FIG. 4a depicts a mapping of a frequency partition to mobile
relay node spatial deployment with FFR across power controlled Un
beams within a donor macro cell according to an exemplary
embodiment;
[0022] FIG. 4b depicts a frequency domain FFR bandwidth
partitioning across Un beams within a donor macro cell according to
an exemplary embodiment;
[0023] FIG. 5a depicts a mapping of frequency partition to mobile
relay node spatial deployment with FFR across power controlled Un
beams within a donor macro cell with a dedicated Channel State
Information Reference Signal according to an exemplary
embodiment;
[0024] FIG. 5b depicts a frequency domain FFR bandwidth
partitioning across Un beams within a donor macro cell according to
an exemplary embodiment;
[0025] FIG. 6 depicts a mapping of frequency partition to mobile
relay node spatial deployment with FFR across power controlled Un
beams within a donor macro cell wherein the mobile relay node is
attached to the nearest Pico Cell/Remote Radio Head of the donor
macro cell according to an exemplary embodiment;
[0026] FIG. 7 is a flowchart of a method for mitigating
interference between Un and Uu transmissions between one or more
mobile relay nodes and one or more stationary nodes in a
heterogeneous network according to an exemplary embodiment; and
[0027] FIG. 8 depicts an exemplary base station for implementing an
interference mitigation system for mobile relay nodes according to
an exemplary embodiment.
DETAILED DESCRIPTION
[0028] The following detailed description of the exemplary
embodiments refers to the accompanying drawings. The same reference
numbers in different drawings identify the same or similar
elements. Also, the following detailed description does not limit
the invention. Instead, the scope of the invention is defined by
the appended claims.
[0029] Reference throughout the specification to "one embodiment"
or "an embodiment" means that a particular feature, structure, or
characteristic described in connection with an embodiment is
included in at least one embodiment of the present invention. Thus,
the appearance of the phrases "in one embodiment" on "in an
embodiment" in various places throughout the specification is not
necessarily referring to the same embodiment. Further, the
particular feature, structures, or characteristics may be combined
in any suitable manner in one or more embodiments.
[0030] To address, for example, issues raised in the Background
section, a general exemplary embodiment includes use of a
combination of fractional frequency reuse (FFR) and power
controlled targeted beamforming to mitigate interference between
transmissions from mobile relay nodes and transmissions from the
underlying heterogeneous network. Prior to discussing specific
exemplary embodiments, a brief discussion of relay technology is
provided for context with respect to FIG. 2b.
[0031] As seen therein, a relay 250 is characterized by (a) its
ability to transmit radio communication signals to, and receive
radio communication signals from, a user equipment 252 (e.g., a
mobile station) over an air interface and (b) its ability to
transmit radio communication signals to, and receive radio
communication signals from, a base station 254 (sometimes referred
to as a "donor" base station). Unlike the base station 254, whose
backhaul link 256 is typically implemented as a physical link
connected to a core network node 258, relay 250's backhaul link 260
(including an uplink 262 and downlink 264) is a wireless backhaul
link. In LTE standardization nomenclature, a relay's wireless
backhaul link 260 is referred to as the "Un" link, and a relay's
wireless radio access link 266 is referred to as the "Uu" link.
[0032] Different types of relay technology can be used to implement
relay 250. For example, a first type of relay (sometimes called a
"repeater" or Layer 1 relay) operates to amplify received radio
signals without performing any other processing on the signals.
Another type of relay (sometimes called a Layer 2 relay) operates
to demodulate/decode and encode/modulate radio signals prior to
amplification and retransmission in order to reduce amplification
of received noise. A third type of relay (sometimes called a Layer
3 relay) performs even more signal processing on received radio
signals than a Layer 2 relay, e.g., ciphering and user-data
concatenation/segmentation/reassembly, and provides a benefit that
the resulting relay air interfaces are very similar to those
associated with typical base stations and have a higher degree of
conformance with standardized approaches. For the purposes of this
discussion, the term "relay" is used generically to include these
(and other) relay technologies.
[0033] Of particular interest for the embodiments described below
are mobile relay nodes. As used herein, the phrases "mobile relay"
or "mobile relay node" refer to relays which are disposed on
movable objects or platforms and which are capable of operating to
relay wireless radio signals between base stations and mobile
stations while changing position or location. One non-limiting
example of such a movable object or platform is a train, however
others will be apparent to those skilled in the art. Moreover, it
should be noted that the phrases "mobile relay" and "mobile relay
node" as used herein do not necessarily mean that the relay nodes
(or the moveable objects or platforms to which the relay nodes are
attached) are moving constantly. Mobile relays or mobile relay
nodes as described herein may, at times, be stationary, e.g., when
a train reaches a stop.
[0034] With this context in mind, three specific exemplary
embodiments will now be discussed in detail, and can be generally
characterized as 1) a mobile relay node intra-cell Un-to-Uu FFR for
which the FFR is implemented within a donor macro cell between Un
and Uu transmissions in combination with power controlled
beamforming on the Un link between mobile relay nodes and eNBs,
wherein the FFR partition can be across the Un and Uu
transmissions, and also more generally, the FFR partition can
further comprise the individual Un beams to the serving eNB; 2) a
mobile relay node inter-cell Un-to-Uu FFR for which the FFR is
implemented across Un and Uu links between neighboring donor macro
cells in combination with power controlled beamforming of the Un
link; and 3) a mobile relay node Un link which is assigned to the
nearest remote radio head of the donor macro cell in which the
mobile relay node resides. However, those skilled in the art will
appreciate that the discussion of these specific embodiments is
meant to be purely illustrative, rather than restrictive, of the
invention.
[0035] Looking first to FIGS. 3a and 3b, an exemplary embodiment
using intra-cell Un-to-Uu FFR in combination with power controlled
beamforming 300 is depicted and illustrates, among other things,
the mapping of frequency regions to the spatial areas of the donor
macro cell 302, 304, 306 and mobile relay nodes 308-324. FIG. 3a is
used to illustrate exemplary beamforming, while FIG. 3b illustrates
exemplary FFR which can be implemented in this embodiment. Starting
with FIG. 3a, the beamforming 332, 334, 336 of the mobile relay
node Un link to the donor eNB 326, 328, 330 mitigates interference
between Un and Uu transmissions within the donor macro cell 302,
304, 306. It should be noted in the exemplary embodiment that FFR
is implemented within each donor macro cell between Un and Uu
transmissions in addition to having power controlled directive
beamforming 332, 334, 336 on the Un links between the mobile relay
nodes and the eNBs 326, 328, 330. It should further be noted in the
exemplary embodiment that although the description provided herein
is for the uplink, the same approach applies equally to the
downlink.
[0036] Looking now to FIG. 3b, an exemplary partitioning used in an
FFR scheme in conjunction with the beamforming of FIG. 3a is shown.
Therein, for a given bandwidth 350, dedicated frequency resource
blocks (RBs) 352, 354 are assigned to the Un links between the
donor eNB and the mobile relay node and separate dedicated
frequencies are assigned within the relay node coverage area. It
should be noted in the exemplary embodiment that the donor macro
cell can assign frequency resource blocks across the entire
available frequency band 356. It should further be noted in the
exemplary embodiment that although the description is for the
uplink, the same approach applies equally to the downlink.
[0037] The exemplary embodiment of FIGS. 3a and 3b allows for
flexibility in the assignment of resources in the donor macro cell
within the time dimension and does not require any fixed Un versus
Uu timing boundaries and/or synchronization to mitigate the
Un-to-Uu interference. Accordingly, Un and Uu transmissions can be
unsynchronized in the time domain, both within a given mobile relay
node and between different mobile relay nodes connected to the same
donor macro eNB, and Un-to-Uu interference will be mitigated.
[0038] As the mobile relay node approaches the donor macro cell,
the Un link can be dynamically power controlled to minimize Un
transmit power based on a number of metrics available in the LTE
standard, such as the Reference Signal Received Power (RSRP), or
Reference Signal Received Quality (RSRQ) of a Channel State
Information (CSI) Reference Signal (RS) measurements of the donor
macro cell at the mobile relay node. Further in the exemplary
embodiment, the power control setting can be targeted to compensate
for path loss or fractional path loss of the mobile relay node Un
link.
[0039] In another aspect of the exemplary embodiment, the power
control setting of the mobile relay node Un link can be optimized
to minimize the interference power to neighboring donor macro
cells. It should be noted in the exemplary embodiment that the
optimization can be based on factors such as, but not limited to,
maximization of Signal-to-Leakage and Noise Ratio (SLNR). Looking
to the uplink side of the exemplary embodiment, Physical Uplink
Shared Channel (PUSCH) or Physical Uplink Control Channel (PUCCH)
data can be employed for power control calculations at the base
station. Alternatively, or additionally, if the mobile relay node
is not transmitting data, then a Sounding Reference Signal (SRS)
can be employed to determine power control settings.
[0040] In another aspect of the exemplary embodiment, a unique
channel state information reference signal (CSI-RS) can be assigned
to each multiple mobile relay node within a donor macro cell to
allow the donor macro cell eNB to differentiate multiple mobile
relay nodes within a donor macro cell. In a further aspect of the
exemplary embodiment, A3 and A4 type event messages can be employed
to trigger selection of the FFR beamformed Un link. It should be
noted in the exemplary embodiment that the above described
techniques can be used in conjunction with relay node sub-frame
multiplex mapping as described in the 3GPP Technical Specification
36.216, "E-UTRA Physical Layer for Relaying Operation," version
10.3, incorporated herein by reference.
[0041] Turning now to FIG. 4a, another exemplary embodiment 400
depicts the exemplary embodiment of FIG. 3a with the further
enhancement of having each Un beam between the donor macro cell eNB
402, 404, 406 and the mobile relay nodes 408-424 within the donor
macro cell 426, 428, 430 coverage area allocated a different
frequency partition 454, 456, 458. Continuing with the exemplary
embodiment, the assignment of separate power controlled beams to
each mobile relay node 408-424 Un link can be identified with the
assignment of a unique channel state information reference signal
to each mobile relay node 408-424. It should be noted in the
exemplary embodiment that FFR in combination with power controlled
beamforming is implemented in each donor macro cell 426, 428, 430
between Un and Uu transmissions and each individual Un link, i.e.,
mapping of frequency regions to the spatial area of the donor macro
cell 426, 428, 430 and mobile relay nodes 408-424.
[0042] Looking now to FIG. 4b, an exemplary embodiment depicts an
FFR frequency partitioning 450 which can be used in conjunction
with the beamforming described above with respect to FIG. 4a.
Therein, dedicated frequency partitions 452, 454, 456, 458
comprised of one or more Resource Blocks (RBs) are assigned to the
Un links between the donor macro cell eNB 402, 404, 406 and the
mobile relay node 408-424 and separate dedicated frequencies are
assigned within the mobile relay node coverage area. It should be
noted in the exemplary embodiment that the donor macro cell can
assign resource blocks across the entire available frequency band
460. It should further be noted in the exemplary embodiment that
although the description is for the uplink, the same approach
applies equally to the downlink.
[0043] In another aspect of the exemplary embodiment, flexibility
of the assignment of resources in the donor macro cell 426, 428,
430 within the frequency dimension is sacrificed to provide
additional interference mitigation between Un links within a donor
macro cell 426, 428, 430. It should be noted in the exemplary
embodiment that this is beneficial during, for example, time
intervals of simultaneous transmissions from different mobile relay
nodes 408-424, within the same donor macro cell 426, 428, 430, to
the donor macro cell eNB 402, 404, 406 for which the spatial
separation is not adequate to ensure the interference is mitigated,
i.e., when two mobile relay nodes 408-424 within the same donor
macro cell 426, 428, 430 have their Un links to the donor macro
cell eNB 402, 404, 406 spatially overlapping.
[0044] Turning now to FIG. 5a, an exemplary embodiment 500
mitigates interference between both Un-to-Un and Un-to-Uu
transmissions and between donor macro cells 502, 504, 506 when Un
and Uu transmissions are unsynchronized and in close proximity
based on the relative locations of mobile relay nodes 508-524 at
the donor macro cell border 526 between different donor macro cells
502, 504, 506. Continuing with the exemplary embodiment, three
different frequency regions are mapped to the different spatial
areas of the wireless backhaul uplinks used in conjunction with the
three different donor macro cells 502, 504, 506 and a fourth
different frequency region is used in the spatial areas associated
with the wireless access links associated with the mobile relay
nodes 508-524 in all three donor macro cells, as indicated in FIG.
5a by the different shadings in the ellipses representing uplink
transmission energy areas between each of the mobile relay nodes
and their respective donor macro cells and the circles representing
uplink transmission areas between each of the mobile relay nodes
and mobile stations. FIG. 5b depicts the above-described FFR
frequency partitioning 550 of FIG. 5a in a different way, i.e.,
dedicated frequency partitions of resource blocks 560, 562, 564 are
assigned to the Un links between the donor macro cell eNB 528, 530,
532 and those of the mobile relay nodes 508-524 which are currently
located with a respective donor macro cell and a separate dedicated
frequency partition 558 is assigned for the mobile relay nodes'
508-524 coverage areas. It will be appreciated that the usage of
three donor macro cells in this embodiment is purely exemplary and
that more or fewer cells can be implemented in a similar manner in
a given system implementation.
[0045] Thus, according to this exemplary embodiment, the Un links
within a donor macro cell achieve orthogonality through the use of
power controlled beamforming, whereas inter-donor macro cell Un
links are isolated based on assigning separate partitions 560, 562,
564 of the FFR scheme. It should be noted in the exemplary
embodiment that each mobile relay node Un link beam can be assigned
a unique channel state information reference signal for power
control purposes. It should further be noted in the exemplary
embodiment that the assignment of the channel state information
reference signal resources between neighboring donor macro cell
eNBs 528, 530, 532 can be coordinated to ensure that mobile relay
nodes in close proximity and belonging to different donor macro
cells 502, 504, 506 have unique channel state information reference
signal resources to identify the mobile relay node 508-524 Un beam.
It should be noted in the exemplary embodiment that as described
for the previous embodiments, the assignment of resource blocks to
user equipment served by any of the donor macro cells 502, 504, 506
can employ any desired resource block within the frequency
band.
[0046] Next in the exemplary embodiment, within a mobile relay node
coverage area, the Uu transmissions can be configured to use both
the common Uu frequency partition as well as the donor macro cell
Un frequency partition if the Un and Uu transmissions of a given
mobile relay node are orthogonal in time. It should be noted in the
exemplary embodiment that if the Un and Uu transmissions of a given
mobile relay node maintain their given frequency partitions, the Un
and Uu transmissions can occur simultaneously even though the
implementation of the duplexer in the mobile relay node would be
challenging and expensive. In the exemplary embodiment however,
with the availability of frequency bands within a given mobile
relay node, simultaneous transmission and reception of the Un and
Uu communications is possible without the requirement of an
expensive and powerful duplexer. It should be noted in the
exemplary embodiment that temporary guard bands can be used to
separate the Un transmissions from the Uu transmissions. It should
further be noted in the exemplary embodiment that although the
description is for the uplink, the same approach applies equally to
the downlink.
[0047] In another aspect of the exemplary embodiment, the frequency
partition boundaries can be fixed but not necessarily equal in the
number of resource blocks. In a further aspect of the exemplary
embodiment, the frequency partition boundaries can be dynamically
selected based on the relative proportional traffic expected for
the given partition. It should be noted in the exemplary embodiment
that the relative proportional traffic is defined as the offered
traffic load within the partition divided by the available capacity
of the communications link.
[0048] Looking now to FIG. 6, an exemplary embodiment expands on
the previously described exemplary embodiments for a heterogeneous
network comprised of donor macro cells 602, 604, 606 and smaller
cells such as, but not limited to, pico cells/remote radio head 608
overlay nodes. It should be noted in the exemplary embodiment that
the spatial topology of such a heterogeneous network design can be
exploited to minimize the interference generated by the mobile
relay node 610 Un backhaul links by linking the mobile relay node
610 Un link to the nearest donor macro cell eNB 612 or pico
cell/remote radio 608 head of the heterogeneous network.
[0049] In another aspect of the exemplary embodiment, any
combination of the features described in the foregoing embodiments
can be selectively or dynamically implemented upon the occurrence
of one or more triggering events. In this context a triggering
event can be based on one or more of, for example, Un power levels,
SINR, SLNR or other metrics associated with the Uu link for the
user equipment reaching a predefined criteria. As a specific, but
non-limiting, illustrative example, triggering logic could, for
example, be implemented to initiate various aspects of FFR and
beamforming associated with mobile relay nodes as follows:
[0050] 1) if the mobile relay node Un power level is greater than a
first predefined threshold then employ fractional power
control;
[0051] 2) otherwise, if the mobile relay node Un power level is
greater than a second predefined threshold or if the macro Uu SINR
is less than a third predefined threshold then employ dedicated
beamforming and/or intra-cell Un FFR;
[0052] 3) otherwise, if the SINR of a mobile relay node Un link is
less than a fourth predefined threshold then employ intra-cell FFR;
and
[0053] 4) if the SLNR of a Uu or of the user equipment associated
with the donor macro cell is greater than a fifth predefined
threshold, then employing inter-cell FFR for the mobile relay node
Un link. It should be noted in the exemplary embodiment that the
features described above can be implemented using any desired
combination of hardware and/or software, e.g., having an engine
component and a command component and that the division of
capabilities between the components can be divided in any fashion
suitable to the implementation.
[0054] Looking now to FIG. 7, a flowchart depicts an exemplary
method 700 for mitigating interference associated Un transmissions
and Uu transmissions between one or more moving mobile relay nodes
and one or more stationary nodes in a heterogeneous network.
Therein, at step 702, fractional frequency reuse is applied between
backhaul (e.g., Un) links and radio access (e.g., Uu) links
associated with mobile relay nodes. It will be appreciated by those
skilled in the art, based upon the foregoing discussion of
exemplary embodiments, that the level of interference varies as the
mobile relay nodes traverse the coverage area of the cell and can
be at its greatest when a mobile relay node is, for example,
approaching cell boundaries and/or proximity of other mobile relay
nodes associated with neighboring donor macro cells. Continuing
with the exemplary method embodiment of FIG. 7, at step 704 a power
controlled targeted beamforming system is applied to the wireless
backhaul links associated with the mobile relay nodes.
[0055] From the foregoing discussion of various exemplary
embodiments, it will be appreciated that these and other
embodiments will, when implemented, have impacts on various nodes
in a radio communication system. For example, the various FFR
schemes described above may need to be implemented at both the
macro donor base station (e.g., eNB) and the mobile relay node. The
beamforming described above can be implemented at the macro donor
base station on both (or either of) the downlink and uplink, and
may also be implemented at the mobile relay node on the uplink.
[0056] Accordingly, FIG. 8 illustrates an example of a base station
800 in which aspects of the above-described embodiments can be
implemented, although a base station is only one example of a
suitable node in which such embodiments can be implemented. This
exemplary base station 800 includes radio circuitry 810 operatively
connected to one or more antennas (or antenna arrays) 815 and to
processing circuitry 820 and memory 830, which are disposed within
a housing 835. In some variants, the radio circuitry 810 is located
within the housing 835, whereas in other variants, the radio
circuitry 810 is external to the housing 835. A network interface
840 is provided to enable the base station 800 to communicate with
other network nodes (not shown), including other base stations. The
processing circuitry 820 is configured to transmit and receive, for
example and via the radio circuitry 810, radio signals toward and
from UEs, relay nodes and mobile relay nodes and can include one or
more processors. As described above, e.g., with respect to FIGS.
3-7, base station 800 can be configured to implement FFR and/or
power controlled beamforming with respect to mobile relay nodes. A
mobile relay node could be depicted in a manner similar to that of
base station 800 in FIG. 8, except that network interface 840 would
then be implemented as a wireless transceiver in support of the
mobile relay node's wireless backhaul link.
[0057] Base station 800 can include a variety of computer readable
media which store program instructions usable to configure
processing circuitry 820 to perform the functions described above.
Computer readable media can be any available media that can be
accessed by processing circuitry 820. By way of example, and not
limitation, computer readable media can comprise computer storage
media and communication media. Computer storage media includes
volatile and nonvolatile as well as removable and non-removable
media implemented in any method or technology for storage of
information such as computer readable instructions, data
structures, program modules or other data. Computer storage media
includes, but is not limited to, RAM, ROM, EEPROM, flash memory or
other memory technology, CDROM, digital versatile disks (DVD) or
other optical disk storage, magnetic cassettes, magnetic tape,
magnetic disk storage or other magnetic storage devices, or any
other medium which can be used to store the desired information and
which can be accessed by processing circuitry 820. Communication
media can embody computer readable instructions, data structures,
program modules and can include any suitable information delivery
media.
[0058] The above-described exemplary embodiments are intended to be
illustrative in all respects, rather than restrictive, of the
present innovation. Thus the present innovation is capable of many
variations in detailed implementation that can be derived from the
description contained herein by a person skilled in the art. All
such variations and modifications are considered to be within the
scope and spirit of the present innovation as defined by the
following claims. No element, act, or instruction used in the
description of the present application should be construed as
critical or essential to the invention unless explicitly described
as such. Also, as used herein, the article "a" is intended to
include one or more items.
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